Three History Analysis And Hydrocarbon Accumulation Of Early Cretaceous Basin In Wunite Depression,Erlian Basin

Wunite depression is located in the northeast of Erlian Basin.With its complex tectonic characteristics and evolution history,there are different degrees of research in the depression and the research results of three histories are relatively scarce.In this paper,basin tectonic assemblage and secondary sag classification of Early Cretaceous in Wunite depression are studied on the basis of structural evolution system in the study area.Typical sags are screened.Vitrinite reflectance,interval transit-time and fluid inclusion data are applied to restore the denudation amount in critical period,paleogeotemperature and maximum paleo-geotemperature in hydrocarbon source rock reservoir-forming period.Combining with the simulation results of three historical on PetroMod software,the burial history,thermal evolution history and hydrocarbon generation history of the study area are analyzed,and meanwhile the structural control of the study area is further discussed.The purpose is to supplement the deficiencies of the three histories of the study area and to provide basic geological data and theoretical support for the exploration and exploitation of oil and gas reservoirs in the study area.Unite depression is located on the Erlian-Hegenshan Melange Belt and Compound Syncline with NE-NNE trending distribution.Its tectonic development is controlled by the NW-SE trending tension of Early Cretaceous and the nature and direction of the basement.Graben-horst assemblages of different scales paralleled to or inclined to the basement tectonic line.Controlled by the difference of tension direction,the nine secondary sags in the depression can be divided into five types: single fault deep fault trough type,single fault shallow fault trough type,single fault shallow fault super type,double fault deep graben type and double fault shallow graben type.The distribution regularity of denudation in the Tenggeer and Saihantala formations of typical sags in the study area is obviously controlled by tectonic activities.The denudation at the top of Tenggeer formation in single-fault shallow-fault trough,single-fault deep-fault trough and single-fault shallow-fault super-depression tends to decrease from steep slope zone to gentle slope zone,and the denudation at the secondary structural zone is different,however the denudation at the top of Saihantala formation is similar.The different activities of faults in different directions and scales during the structural inversion period determine the denudation amount of different structural parts in the area: NE direction is the main controlling fault,NW direction is the auxiliary regulating fault,primary and secondary faults control the denudation amount distribution of the whole sag and each zone respectively,and tertiary faults play a local regulating effect.The denudation amount of double-fault shallow graben and double-fault deep graben depressions has the tendency of decreasing gradually from the middle graben zone to both sides,and the secondary faults play the role of local control and regulation.The Early Cretaceous in the study area can be divided into four burial stages: from the Aershan formation to the end of Tenggeer formation,the strata declined and received deposition;from the end of Tenggeer formation,the strata were uplifted and denuded;from the Saihantala formation,the strata were uplifted and denuded.The plane distribution law of sedimentary rate is basically consistent with the sedimentary thickness of the stratum,and the sedimentary rate in the sedimentary center is the largest.The sedimentary centers of single-fault shallow-fault trough,single-fault deep-fault trough and single-fault shallow-fault super-depression are close to the side of the main controlling faults at the boundary,and the sedimentary rates of the two-fault shallowgraben and double-fault deep-graben depressions are gradually decreasing from the steep-slope zone to the gentle-slope zone;the sedimentary centers of the two-fault shallow-graben and double-fault deep-graben depressions are located in the area where the graben is located,Tectonic activity can control the burial history by controlling the sedimentary center,burial depth and denudation in the study area,thus controlling the thermal evolution history and hydrocarbon generation history.The thermal history evolution stage of the Lower Cretaceous is consistent with the burial history.It experienced two stages of increase and decrease.The increase and decrease ranges are positively correlated with sedimentary thickness and denudation,respectively.The maximum palaeogeotemperature is 40-120?.The organic matter evolution of source rocks in Aershan and Tenggeer formations is high,and their distribution pattern is similar to that of burial history.They have two reservoir-forming periods respectively.The area with the largest deposition and denudation controlled by faults in the depression has the characteristics of long hydrocarbon generation time of source rocks,easy hydrocarbon migration,favorable reservoir formation and coincidence with the development area of oil and gas reservoirs,which can provide important enlightenment for the exploration of oil and gas reservoirs in the depression.63 figures and 23 tables were included,and 119 literatures were referenced.